An oil sand usually consists of a mixture of clay substance, silicates, water and hydrocarbons. The oil phase contained up to 18% in oil sands consisting of various hydrocarbons has a very different composition, often specific to the extraction area, wherein bitumen, crude oil and asphalt can be contained therein. The processing of oil sand is carried out with the aim of separating the stone or sand fraction comprising clay substance and silicates from the actual valuable material, i.e., the oil phase comprising the hydrocarbons.
Oil sands are frequently extracted in open cast workings. For extraction from deeper layers of the earth preprocessing is often undertaken, in which the steam is introduced into the deposits, the hydrocarbons are liquefied and collected at drilling rigs and bought to the surface.
U.S. Pat. No. 4,240,897 describes a method for extraction of bitumen from oil sand by means of hot water.
DE 10 2007 039 453 A1 describes a method for obtaining bitumen from oil sand-water mixtures by means of flotation.
According to the CLARK-ROWE process, oil sand is mixed with sodium hydroxide and the oil sand phase is mobilized thereby. A water-oil phase separation is primarily undertaken by flotation. The remaining stone or sand component still contains up to 10% of the oil phase after the extraction, which in part is bound adsorptively to the surface of the finest particles. This leads to a steric stabilization of these particles in the waste water flow of the process, making separation of these particles very much more difficult. Furthermore a significant amount of clay substance is so greatly hydrophobized by an adsorptive agglomeration of the oil phase so that this gets into the product during a flotation, i.e. the separated oil phase. The clay substance represents a quality-reducing contamination there, which can only be separated again with difficulty. Depending on oil sand composition, to obtain a barrel of oil phase around three to four times the amount of non-recyclable fresh water is needed. The water is stored temporarily or finally in collection basins with the separated stone or sand fraction.
U.S. Pat. No. 4,968,412 describes a two-stage method for removal of bitumen from oil sand, in which in a first step organic solvents are supplied and the clay substance is separated. In a second step the processed oil sand is washed with water while adding surfactants.
U.S. Pat. No. 3,542,666 describes a method for extraction of hydrocarbons from oil sand, in which organic solvents in combination with a small amount of water are mixed in specific quantity ratios with the oil sand to a suspension and the pH value of the suspension is set to at least 5 before there is filtration of the suspension.
The unpublished European patent application with the file reference EP 10156735 describes a method for extraction of hydrocarbons from oil sand. It has been shown that a use of purely organic extraction means leads to the finest components which predominantly consist of clay substance agglomerating in the oil sand and the agglomerates additionally exhibiting a hydrophobic behavior. This makes possible a separation of the clay substance with the stone and sand fraction by means of a mechanical solid-liquid filtration. In this process the oil sand is suspended with organic solvents and filtered by means of a continuous filter, especially a drum filter. The filter cake formed is washed in a filter unit by means of at least one first wash liquid and subsequently steamed with a steam formed from a second wash liquid, wherein residues still present in the filter cake of the first wash liquid(s), including possible hydrocarbon residues, are driven out of the oil sand. The filter cake is cleaned and largely dehumidified in this case. In this case the application of the first wash liquid(s) to the filter cake can be undertaken by means of a dispensing device, which e.g. is realized by nozzles. The nozzles here are built into a chamber or a fluid of a steaming unit for steaming the filter cake with the steam consisting of the second wash liquid.
The driving out of the residual amount of first wash liquid from the filter cake is also referred to in the literature as steam pressure filtration.
Basics of steam pressure filtration are known and are described for example in the following publications:
“Steam Pressure Filtration: Mechanical-Thermal Dewatering Process”, U. A. Peuker, W. Stahl, Drying Technology, 19(5), pages 807-848 (2001);
“Applying mechanical-thermal filtration processes for purification, e.g. solvent removal”, U. A. Peuker, Proc. Filtech Europe, 12-23 Oct. 2003, Dusseldorf, Germany;
“Abtrennung von organischen Lösemitteln aus Filterkuchen mit Dampf” (Separation of organic solvents from filter cakes with steam), U. A. Peuker, F & S Filtrieren and Separieren, Volume (2003), No. 5, pages 230 to 236;
“Steam Pressure Filtration for the treatment of limey soils contaminated with aliphatic hydrocarbons”, by M. Bottlinger, H. B. Bradl, A. Krupp, U. Peuker, 2nd Int. Containment & Remediation Technology Conference, 10-13 Jun. 2001, Orlando, Fla., USA.
The filter cake, comprising the stone or sand fraction of the oil sand is freed from first wash liquid when the steam is pushed through it and at the same time a quantity of hydrocarbons or oil phase dissolved therein is driven out. This increases the yields of hydrocarbons or improves the separation degree to around 95 to 98%, which characterizes the separation success.
It has been shown that a combined design of dispensing device and steaming unit is able to be used if the first wash liquid supplied via the dispensing device and the second wash liquid from which the steam is formed are identical or at least similar in relation to the temperatures at which they boil, i.e. do not differ by more than around 5° C. in the boiling temperatures.
However if first and second wash liquids are used which differ by more than 5° C. in their boiling temperatures, undesired condensation or evaporation effects can occur in the chamber or hood of the steaming unit.
When a boiling temperature is referred to in this document this is always to be understood as the boiling temperature of a material under normal pressure.
If for example an organic solvent such as, e.g., ethanol with a boiling temperature of 78° C. is applied to the filter cake as the first wash liquid, and water with the boiling temperature of 100° C. as a second wash liquid is vaporized and the filter cake has the water vapor applied to it, a part of the first wash liquid already vaporizes in the chamber or hood before it has even reached the filter cake. This reduces the washing performance and also leads to an undesired buildup of pressure in the chamber or hood.
If conversely an organic solvent is applied to the filter cake as the first wash liquid, such as, e.g., toluol with a boiling temperature of 110° C. and water with the boiling temperature of 100° C. as the second wash liquid is vaporized and the filter cake has the water vapor applied to it then a part of the water vapor already condenses in the chamber or hood on the first wash liquid before it is even reached the filter cake.
This prevents the dehumidification of the filter cake and leads to an undesired fall in pressure in the chamber or hood.